The invention concerns an automotive construction machine, as well as a method for working ground surfaces.
Such automotive construction machines for working ground surfaces are known, for instance, from EP 1408158 A.
The road milling machine described therein shows a machine frame with a drive engine for driving traveling devices and for driving working devices. The traveling devices may consist of either wheels or crawler tracks, which are connected to the machine frame via lifting columns.
A drum drive drives a milling drum for milling the ground surfaces preferably in up-milling mode. The milling drum is capable of being uncoupled from the drive train by means of a coupling. A scraper blade is located in a height-adjustable manner behind the milling drum when seen in the direction of travel, which can glide on the surface milled or to be milled by the milling drum. In milling mode, the lower edge of the scraper blade is always located at the lowest plane of the cutting circle of the milling drum.
Such construction machines operate in strips in accordance with the width of the milling drum. This means that the construction machine has to travel back after having milled a pre-determined length of ground surface in order to then mill an adjacent strip.
It is necessary that the milling drum is idle when traveling backwards in order to avoid any accidental collision of the tools of the milling drum with the ground surface, because the construction machine may be accelerated suddenly and uncontrollably in case of an inadvertent engagement of the milling drum with the ground surface. The circumferential speed of the milling drum, in particular at operating speed, is many times, for instance, three times that of the travel speed so that the road construction machine may be accelerated forcefully in case of an engagement of the milling drum.
This results in a risk of the milling drum being damaged in case of an accidental engagement with the ground surface, so that the milling drum is first uncoupled from the drive train after it has been raised from the milled cut at the end of a ground surface to be worked. The construction machine can now be driven back to the beginning of the length of ground to be worked, where the speed of the drive engine must be reduced to idle speed first to enable coupling of the milling drum.
Contrary to the engine of a passenger car, a considerable waiting period elapses until the speed of the drive engine, which consists of a combustion engine, has been reduced to idle speed and also until it has been increased to operating speed again.
The combustion engine must then be brought back to operating speed prior to working the next strip. These processes are very time-consuming and very annoying for the machine operator, in particular in case of short stretches of road to be worked. Moreover, the incessant switching operations of the coupling and the related frequent load changes of the combustion engine give rise to increased wear and tear of the coupling, the combustion engine and all components that are part of the drive train.
The purpose of the invention is, therefore, to create a construction machine, as well as a method for working ground surfaces, which is capable of reducing the time required for working a pre-determined ground space.
The invention provides in an advantageous manner that the milling drum, when in raised position and with a direction of travel in which the rotating direction of the milling drum corresponds to the rotating direction of the traveling devices, remains coupled with the drum drive and that a monitoring device monitors a distance between the milling drum and the ground surface and uncouples the raised milling drum from the drive engine and/or uncouples the traveling devices from the drive engine and/or raises the machine frame and/or generates an alarm signal when the monitoring device detects a deviation which falls below a pre-determined distance.
According to the invention, the milling drum can remain coupled with the drive engine in a permanent manner.
It is no longer required to uncouple the milling drum from the drive train when it is raised out of the milled cut. As a result, it is also not necessary to reduce and subsequently increase the speed of the combustion engine in order to engage the milling drum again after repositioning. The milling drum can be removed from the milled cut by swivelling or raising it, for instance, via lifting columns of the traveling devices. When the milling drum is in the raised position, a monitoring device detects as to whether the distance between the raised milling drum and the ground surface, which has been pre-determined for traveling when not in milling mode, is maintained. If the deviation falls below the pre-determined distance, the raised milling drum, which at that time continues rotating, is uncoupled from the drive engine so that, should the milling drum actually come into contact with the ground, the drive power has no effect on the milling drum and only the milling drum's actual kinetic energy of rotation has to be destroyed. When doing so, the mass of the construction machine suffices to prevent the construction machine from carrying out a jump in the direction of travel in case the milling drum inadvertently engages with the ground surface. In this way, it is ensured that no time loss is incurred due to the fact that a reduction and increase of the speed of the drive engine have to be waited for when the construction machine is traveling without being in milling mode.
A further advantage is that the wear and tear of machine elements, in particular of the coupling, the combustion engine and all other components that are part of the drive train, is reduced.
It is preferably provided that the milling drum mills the ground surface in up-milling mode, in which case traveling in forward direction is uncritical as the milling drum rotates in opposition to the direction of travel. The invention concerns itself with traveling in backward direction, in which the milling drum can, contrary to prior art, remain coupled with the drive engine despite the milling drum rotating in opposition to the direction of travel.
Likewise, traveling backwards when the milling drum is in down-milling mode is uncritical due to the milling drum rotating in the direction of travel, and according to the invention, the milling drum, when in raised position, remains coupled with the drive engine also when traveling in forward direction without being in milling mode.
Monitoring of the pre-determined distance by the monitoring device can be effected either directly or indirectly. Direct measuring is effected, for instance, by means of mechanical or electronic measurement of the distance, whereas indirect measuring of the distance can be effected, for instance, via machine elements of the construction machine, via tracers or via the actual position of the lifting column carrying the machine frame.
When doing so, the pre-determined distance between the raised milling drum and the ground surface can be monitored with at least one sensor.
The pre-determined distance to be monitored by the monitoring device may be capable of being increased in accordance with the travel speed of the traveling device. The pre-determined distance can, for instance, be increased proportionally or progressively in accordance with the increasing travel speed.
A preferred embodiment of the invention provides that the milling drum is raised by a pre-determined amount that is larger than a minimum distance to be maintained between the milling drum and the ground surface, and that a sensing device measuring towards the ground surface shows a lower limit position which corresponds to a pre-determined distance or to a minimum distance to be maintained between the milling drum and the ground surface. With such a sensing device, the monitoring device has to merely establish as to whether the sensing device leaves the lower limit position, because in this case a pre-determined distance or a minimum distance to be maintained by the milling drum is no longer adhered to.
The construction machine may be provided with a sensing device that is capable of being lowered relative to the milling drum, the said sensing device projecting vis-à-vis the milling drum towards the ground surface by a pre-determined distance in relation to the lowest point of the cutting circle of the milling drum. With the milling drum in raised position and the sensing device simultaneously in lowered position, the monitoring device generates, for instance, a control signal for uncoupling the milling drum from the drive engine if the at least one sensor detects a contact of the at least one sensing device with the ground surface or that the at least one sensing device is raised by the ground surface. This means that the sensing device, which may in the most simple case consist of a tracer, is simultaneously lowered to a lower limit position while the milling drum is raised, the said lower limit position corresponding to a pre-determined distance or to a minimum distance between the rotating milling drum and the ground surface. When doing so, the sensing device itself maintains a distance vis-à-vis the ground surface. If the sensing device touches the ground surface while the construction machine travels without being in milling mode, or if it is detected that the sensing device is raised by the ground surface, then the monitoring device generates, for instance, a control signal for uncoupling the milling drum from the drum drive or the drive train respectively.
The sensor is capable of detecting a ground contact, for instance, by means of a structure-borne sound sensor, or the position of the sensing device, for instance, by means of a path sensor. As an alternative, the lowest position of the sensing device can be determined by means of a limit switch.
Apart from uncoupling the milling drum, the monitoring device can additionally or alternatively uncouple the traveling devices from the drive engine and/or raise the machine frame and/or set off an alarm signal.
In the raised position of the milling drum, the sensing device is lowered towards the ground surface by a pre-determined amount that is larger than the pre-determined distance between the milling drum and the ground surface. The sensor is capable of at least detecting the lower limit position of the sensing device, with the lower limit position corresponding to, for instance, the minimum distance between the milling drum and the ground surface.
The sensing device may consist of a scraper blade that is arranged behind the milling drum when seen in the direction of travel. The scraper blade is capable of being lowered downwards beyond the lowest position of the cutting circle of the milling drum.
A further alternative provides that the sensing device consists of a hood enclosing the milling drum and/or of a side plate that is arranged at the side next to a front end of the milling drum.
As described previously in connection with the sensing device, the scraper blade, the hood, or the side plates provided for at the front ends of the milling drum can also be lowered beyond the lowest point of the cutting circle of the milling drum in the same way. The position of the side plates, of the scraper blade and of the hood enclosing the milling drum can be monitored with regard to their distance from the ground surface in the same way as previously described in connection with the sensing device.
In case of a hood enclosing the milling drum, the said hood can be lowered relative to the milling drum. Such hood is known, for instance, from WO 97/20109.
In the following, embodiments of the invention are explained in more detail with reference to the drawing.